Method for making masterbatch

ABSTRACT

A process for producing a colouring agent (masterbatch) for colouring a polymer is provided, comprising the step of mixing a plastics material, carbon black and waste print powder. The maximum proportion of waste print powder is preferably 50%. The process enables waste print powder to be recycled in a useful manner, thereby addressing the environmental problem of waste print powder pollution.

[0001] The present invention relates to a process for producing a colouring agent for colouring a polymer, and in particular to a process for producing a masterbatch for use in extrusion processes and the like.

[0002] The development of polymer chemistry and its subsequent application to the production of industrial and household articles is one of the great success stories of the 20^(th) century. The result is that an enormous range of articles are now produced from plastics materials. Some of these were previously produced from alternative materials, and the production of some has only been possible because of the development of polymer chemistry.

[0003] Despite the fact that this technology is more than a century old, the scale of production of these articles is such that research into new and improved polymers and methods of production continues apace.

[0004] The natural colour of most plastics materials is rather unattractive and variable, and accordingly a colouring agent has traditionally been added to the plastics material in order to produce a finished article of uniform colour. When the aesthetic appearance of the article is not particularly important (for example in the production of dustbins or industrial components), then the article is often coloured black. However, it is possible to produce the full range of colours simply by varying the colouring agent in order to meet consumer demand.

[0005] The colouring agent is normally prepared by adding a dyestuff to a plastics material in order to produce a small amount of intensely coloured plastics material, and then by mixing the intensely coloured plastics material with a second plastics material (which may or may not be the same as the first) when the second plastics material is being formed into the finished article. The intensely coloured first plastics material is known as “masterbatch”.

[0006] Black masterbatch is generally formed by mixing carbon black with an appropriate polymer and optionally adding chalk dust as a filler in an extrusion machine. The components are heated, mixed, extruded and pelletised to produce the masterbatch, which is then added in amounts of 0.1 to 25% by weight to the plastics material when it is being processed into the finished article (for example in a moulding or extrusion process).

[0007] If it is desired to produce a masterbatch of a different colour, then an appropriately coloured pigment is mixed with the polymer and chalk filler (normally without carbon black) and the process is carried out as before.

[0008] Industry is always on the lookout for improved production processes, particularly in the field of polymer chemistry with its large scale of production and the consequently large cost savings available.

[0009] EP 0322555 (General Electric Company) discloses a method for colouring thermoplastic polymer resins using a masterbatch which is formed from a colorant such as carbon black and a polyetherimide ester elastomer. A wide variety of inorganic and organic colorants are disclosed. The masterbatch may be manufactured on high intensity high shear equipment such as compounding extruders, two-roll compounding mills and in Banbury mixers.

[0010] WO 79/00406 (Akesson et al.) discloses a method for the preparation of a masterbatch to be added to a thermoplastic resin. The masterbatch is in the form of a colourant including colour pigment particles as an additive dispersed in a vehicle.

[0011] JP 08003322 (Canon KK) discloses compositions for colouring plastics comprised of thermoplastic polymers and pigments. The compositions give mouldings without unevenness or density difference of colour.

[0012] According to a first aspect of the present invention, there is provided a process for producing a colouring agent for colouring a polymer, comprising the step of mixing a plastics material and waste print resin. Optionally, pure carbon black and low density polyethylene may be added.

[0013] Print resin is a specific product used by the print industry to create print automatically and at high speed onto paper (or another substrate) without causing smudging.

[0014] Print resin is normally provided in powder form, and generally comprises at least some of the following components: carbon black, ferrous oxide, carranba wax, styrene acrylic polymer, polyester resin, zinc stearate, nigrazine dye and oxide fumerate powder. A variety of carrier polymers may be included depending on the brand. Ferrous oxide, carbon black and nigrazine dye are black colour enhancers, and one or two of the three may be omitted, depending on the shade of black or brand of powder employed. If a different colour to black is required, then all three are omitted, and a pigment of appropriate colour is added.

[0015] Without wishing to be constrained by theory, it is thought that print powder also includes a component or number of components which stabilises the melting point of the composition. All waste print powders investigated by the applicants (including waste print powders obtained from Xerox, Canon, Ricoh, Hewlett-Packard and Osay) have a melting point close to 118° C.

[0016] As the temperature is raised above the melting point, the waste print powder hardens again. Investigations have found that this solidification point is in all cases very close to 0.75° C. above the melting point, i.e. 118.75° C.

[0017] Print powder is normally provided in a sealed cartridge for use in computer printers and photocopying machines. The cartridge may have a sliding door or the like which opens when the cartridge is fitted into the printer in order to allow access to the waste print powder, and closes when the cartridge is removed from the printer in order to prevent the escape of powder.

[0018] It is impractical to design a system which uses all of the powder in a cartridge and inevitably somewhere in the region of 5% of the powder remains inaccessible in the cartridge when the printer shows the cartridge as having expired.

[0019] Even though the amount of powder remaining in a spent cartridge is relatively small, the total number of spent cartridges and therefore the total amount of waste powder produced by industry is substantial and growing rapidly.

[0020] The powder left in expired cartridges is a waste product which is very difficult to dispose of. The powder is so finely divided (with particle sizes being in the order of 15 μm) that it tends to escape from landfill sites and find its way to the water supply, with serious environmental consequences. This is now of world-wide concern.

[0021] The inventive realisation of the present realisation is that this waste print powder can be used to make masterbatch. Thus, a waste product which is extremely difficult to dispose of in an environmentally friendly way can be employed in the production of an industrially useful product.

[0022] A substantial amount of surplus or imperfect waste print powder is produced by print manufacturers, and often this is difficult or expensive for the manufacturer to dispose of Accordingly, the powder employed in the present invention may be obtained from spent cartridges as described above, or may be obtained directly from the print manufacturer, who may have supplies which could not otherwise be used in print cartridges. For example, waste powder for printer cartridges must be produced with having narrow particle size distribution. Powder having particles which are too small (in the order of 2 μm or less) or too large (in the order of 10 μm or more) cannot be employed in printer cartridges and is surplus to requirements. It is however perfectly suitable for the purposes of the present invention.

[0023] The preferred proportion by weight of the components in the inventive process is as follows:

[0024] Plastics materials—preferably from 5 to 95%, more preferably at least from 20 to 50%, most preferably about 25%.

[0025] Carbon black—preferably from 0.5 to 80%, more preferably from 20 to 40%, most preferably about 25%.

[0026] Waste print powder—preferably from 5 to 80%, more preferably from 25 to 50%, most preferably about 40%.

[0027] The ratio of plastics material to carbon black depends on the particle size of the carbon black. Thus the ratios of particularly preferred embodiments of the present invention are given in Table 1 below: TABLE 1 % % % CARBON BLACK CARBON PLASTICS WASTE PRINT DBP STRUCTURE BLACK MATERIAL POWDER 170 20 35 45 137 22.5 32.5 45 115 25 30 45 70 30 25 45 65 32 23 45 55 35 20 45

[0028] The term “Carbon Black DBP Structure” refers to the grade of carbon black and is a definition well known in the industry.

[0029] If these ratios are not adhered to, the likelihood is that:

[0030] (1) the end product will be too brittle to be effective

[0031] (2) the product will overheat during the process and the mixture will oxidise

[0032] (3) if oxidation does occur the pigment transportation qualities of the product are reduced to below commercial value.

[0033] It has been found that the use of waste print powder on its own results in an end product which is too brittle to be effective.

[0034] The relative proportions of the various components is varied depending on how dark the masterbatch is required to be (the so-called “cover”). For example, if heavier cover is required than that given by the preferred proportions of 50% waste print powder, 25% carbon black and 25% polymer, then 45% waste print powder, 30% carbon black and 25% polymer may be used. Ideally, the polymer is included at 25% by weight or more, which prevents the final product becoming brittle and difficult to handle during extrusion.

[0035] Other additives may be included to create and/or enhance the required end-product specification.

[0036] In order to produce a non-black colouring agent, the appropriate coloured pigment (e.g. coloured waste print powder) is mixed with the plastics material in accordance with the invention. The coloured powder may be supplemented with additional pigment and/or other additives, in order to produce the desired final colour.

[0037] An effective masterbatch can be prepared by the following preferred process:

[0038] 1. The components are mixed loosely in a drum.

[0039] 2. The components are transferred by a variable speed feeder at a defined rate to a mixer and grinder where they are mixed, ground and amalgamated.

[0040] 3. The resulting materials exit the pre-mixer in a rope form which is then fed by a time-sequenced pusher device at a constant rate into an extruder.

[0041] 4. The mixture is mixed and extruded as a series of strands.

[0042] In a preferred embodiment, the components are mixed together and heated in a mixing machine such as a twin screw extruder, a single screw extruder, a two roll mill, or, preferably, a Farrel CP machine, a Banbury mixer, or any suitable mixer.

[0043] It has been found that it is advantageous to keep the entrance into the mixer relatively cool in order to avoid softening the waste print powder (which softening begins at about 90° C.). Keeping the entrance below about 90° C., preferably from 40 to 90° C. and most preferably about 45° C., enables the waste print powder to be transported into a mixer in a stable condition. It is particularly desirable to control this temperature carefully in the case of mixers other than Banbury or Farrel CP machines. The advantage of using a Banbury or Farrel machine is that mixing of the components is more thorough and the entrance temperature is not so critical.

[0044] Processing temperatures within the mixer are fairly flexible, but preferably range from 135 to 230° C. and are most preferably at about 150° C. At approximately 118° C., the waste print powder melts and then very rapidly hardens as the temperature rises by another degree or so. It is therefore necessary to use a mixer which is sufficiently powerful to grind the powder continuously to prevent it from conglomerating and hardening. The mixer should be sufficiently powerful to mix the waste print powder and the carbon black into the carrier resin homogeneously. It has been discovered that the Banbury and Farrel machines are particularly effective at achieving this aim.

[0045] In a preferred embodiment, the components are mixed at a mixing rate of from 150 to 500 min⁻¹, preferably from 350 to 400 min⁻¹.

[0046] Because the processing temperature tends to range from 135 to 230° C., heat is transferred from the main body of the mixer to the mixer entrance. Accordingly, the mixer entrance may be artificially cooled, for example by circulating cooled water in a jacket around the entrance, in order to maintain the entrance at the temperatures outlined above.

[0047] The components are fed into the mixer until the maximum safe operational amperage is reached. In the case of a Farrel CP 500, the maximum amperage is in the region of 90 to 95 amps and this equates to a rate of addition of the mix of from 500 to 550 kg per hour.

[0048] The plastics material may be selected by a skilled person to match the plastics material which is to be coloured by addition of the masterbatch. Suitably plastics material include polyethylene, polypropylene, EVA, EEA, ABS, PVC or any other type of polymer.

[0049] After the components have been mixed to form the masterbatch, the masterbatch may be extruded and divided into pellets for use in the colouring of a second plastics material.

[0050] In accordance with a second aspect of the invention, there is provided a colouring agent for colouring a polymer which agent is obtainable by means of a process defined above.

[0051] In accordance with a third aspect of the invention, there is provided a process for forming a coloured object from a plastics material, comprising the steps of mixing said plastics material with a colouring agent obtainable by means of a process as defined above, and forming the coloured plastics material into said object. The object may be formed by means of an extrusion or moulding process.

[0052] The amount of masterbatch added to the plastics material generally varies from 1 to 25% by weight. The precise amount will depend on the level of cover required, and from what the plastics material is formed. For example, if the plastics material is clear, then a relatively low amount of masterbatch is required (perhaps 1-2%) in order to produce a good level of cover. If however plastics material is used which has been coloured white (with e.g. titanium dioxide), then perhaps 15-20% of masterbatch may be required in order to achieve the same level of cover. Cover is usually assessed by eye and the components of the subsequent process adjusted accordingly.

[0053] In a fourth aspect of the invention, there is provided an object formed from a plastics material, which material has been coloured by the addition of a colouring agent obtainable by means of a process as defined above.

[0054] The invention will now be illustrated by means of the following examples.

EXAMPLE 1

[0055] Carbon black, print powder from expired printer cartridges and manufacturer's waste and polyethylene resin were weighed and loaded into a blender above an extruder in the following amount:

[0056] Carbon black—25%

[0057] Print powder—50%

[0058] Polyethylene—25%

[0059] After being blended the mixture was fed into a Farrel CP 500 mixer at a feed rate of from 350 to 550 Kgph.

[0060] The entrance to the mixer as surrounded with a water-cooled jacket in order to maintain the temperature at about 60 to 70° C.

[0061] The components were mixed at high pressure within the Farrel CP 500 at approximately 150° C. and at a mixing speed of from 350 to 400 revolutions per minute.

[0062] The resultant mix was discharged from the mixer in the form a continuous hot rope into a single screw extruder. It was then pushed through a dye to form separate strands, which were fed into a pelletiser where pellets were formed and cooled.

EXAMPLE 2

[0063] The process of Example 1 was carried out except that the proportions of the components were altered to the following in order to provide masterbatch with a heavier cover:

[0064] Carbon black—30%

[0065] Waste print powder—45%

[0066] Polyethylene—25%

[0067] Machine settings are within parameters as defined in Example 1. 

1. A process for producing a colouring agent for colouring a polymer, comprising the step of mixing a plastics material, carbon black and waste print powder.
 2. A process as claimed in claim 1, wherein the proportion by weight of the components is from 5 to 95% plastics material, from 0.5 to 80% carbon black, and from 5 to 80% waste print powder.
 3. A process as claimed in claim 2, wherein the said proportions are from 20 to 50% plastics material, from 20 to 40% carbon black and from 25 to 50% waste print powder.
 4. A process as claimed in claim 2, wherein the said proportions are about 25% plastics material, about 25% carbon black and about 40% waste print powder.
 5. A process as claimed in any preceding claim, wherein the components are added to a mixer, and wherein the entrance to the mixer is maintained at a temperature of from 40 to 90° C. to prevent softening of the waste print powder.
 6. A process as claimed in claim 5, wherein the mixer entrance is maintained at about 45° C.
 7. A process as claimed in any preceding claim, wherein the components are mixed at a temperature of from 135 to 230° C.
 8. A process as claimed in claim 7, wherein the components are mixed at about 150° C.
 9. A process as claimed in any preceding claim, wherein the components are mixed in a twin screw extruder, a Farrel CP machine, a Banbury mixer, a single screw extruder, or a two roll mill.
 10. A process as claimed in claim 9, wherein the components are mixed at a mixing rate of from 150 to 500 min⁻¹.
 11. A process as claimed in any preceding claim, wherein after the components are mixed to form the colouring agent, said agent is extruded and divided into pellets for use in the colouring of a second plastics material.
 12. A colouring agent for colouring a polymer which agent is obtainable by means of a process according to any preceding claim.
 13. A process for forming a coloured object from a plastics material, comprising the steps of mixing said plastics material with a colouring agent as claimed in claim 12, and forming the coloured plastics material into said object.
 14. A process as claimed in claim 13, wherein said object is formed by extruding said plastics material with said colouring agent.
 15. A process as claimed in any preceding claim, wherein the waste print powder melts at about 118° C. and solidifies at about 118.75° C.
 16. An object formed from a plastics material, which material has been coloured by the addition of a colouring agent as claimed in claim
 12. 